1. Field of the Invention
This invention relates to an ultra-sonic dog-expelling device, and particularly to a device which is portable, and which can generate an intermittent oscillation frequency to interfere and annoy the hearing sense of a dog to be expelled.
2. Description of the Prior Art
Recently, there are a lot of cur dogs loitering in many streets, and a lot of private-fed fierce dogs which are causing a passer-by, visitors, a postman or a deliveryman fear to be bitten by them. Therefore, the safety of the aforesaid persons may be protected by carrying such ultra-sonic dog-expelling device so as to prevent from being attacked by a cur dog. During the highly developed scientific era, it has been proved that the high frequency of ultra-sonic wave can effectively expel a dog without any environmental pollution, and such dog-expelling device has widely been interested by people.
However, the conventional ultra-sonic dog-expelling device comprises a circuit to generate a continuous ultra-sonic wave, which is subject to causing a dog to adjust itself to such continuous sound, i.e., the dog-expelling effect can be reduced considerably after a period of time; further, to generate a continuous ultra-sonic wave usually consumes a lot of electric power, and therefore the battery thereof must be replaced quite often. Moreover, the current dog-expelling device usually has a complicate structure which causes inconvenience when a user replaces the battery thereof. In addition, the big size of the device causes inconvenience for a user to carry such a device or simply put it in a pocket.